Which wire is power on thermostat?

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Besides, where does thermostat get power?

Most room thermostats on heating and cooling systems receive their 24V DC electrical power from a low voltage transformer that itself is usually found at the boiler or furnace (blue arrow in our photo at left).

Beside above, how are thermostats wired? Power from the air-conditioning transformer comes into the terminal labeled RC. The ball controlled by the mode switch jumps the current onto a trace that leads to the terminal in the lower-right corner of the circuit board. This terminal connects to the top layer of the thermostat through a screw.

Beside above, what is the blue wire on a thermostat?

The blue wire, or C-wire, is known as the common wire. It's there to provide power to the thermostat. Older thermostats usually don't have a C-wire because they either don't need power or, if they do, they get it from a battery. Modern thermostats are a different story.

Is the C wire a ground?

The C wire is the common wire ground wire. You already have 24v ac going to the red wire. If you have an extra wire connect it to the C at the thermostat and ground it at the transformer box in the AC unit.